The present invention relates to an organic thin film EL (ElectroLuminescence) panel and, more particularly, to the structure of a metal electrode in an EL panel and a method of manufacturing the same.
An organic thin film EL element is a light-emitting element having a transparent support substrate, transparent electrode, organic thin film, and metal electrode. The transparent support substrate is made of, e.g., glass. The transparent electrode is formed on the transparent substrate and made of, e.g., ITO (Indium Tin Oxide). The organic thin film is comprised of a hole transport layer, a light-emitting layer, and an electron transport layer, and is formed on the transparent substrate including the transparent electrode. The metal electrode is formed on the organic thin film and made of a metal having a small work function. In the organic thin film EL element having this arrangement, when the transparent electrode is set at a positive voltage and a DC voltage of about 10 V is applied across the transparent electrode and the metal electrode, holes emitted from the transparent electrode and electrons emitted from the metal electrode are recombined with each other in a light-emitting layer to emit light. Therefore, light is emitted from the transparent support substrate.
The transparent electrode has the function of an anode and a function of transmitting emitted light therethrough, and is mainly made of ITO. The hole transport layer has a function of facilitating hole injection from the anode, a function of transporting holes, and a function of interfering with electrons. To form the hole transport layer, tetraphenyldiamine (TPD), a hydrazone derivative, a triazole derivative, polythiophene, or the like is used. The light-emitting layer has a hole and electron injecting function, a hole and electron transporting function, and a light-emitting function by recombination of the holes and electrons. To form the light-emitting layer, an organic metal complex such as tris(8-quinolilite)aluminum, quinacridone, rubrene, perylene, or the like is used.
The electron transport layer has a function of facilitating electron injection from the metal electrode, an electron transport function, and a hole interfering function. To form the electron transport layer, an organic metal complex such as tris(8-quinolilite)aluminum, a perylene derivative, a pyridine derivative, a quinoline derivative, or the like is used. The metal electrode has the function as a cathode. To effectively perform electron injection, the metal electrode is made of a metal element, e.g., lithium, magnesium, aluminum, or silver, having a small work function alone, or of a magnesium-silver alloy or lithium-aluminum alloy to improve the stability.
FIGS. 8A and 8B show the arrangement of a conventional dot matrix color organic thin film EL panel using such an organic thin film EL element.
Referring to FIG. 8B, a plurality of transparent electrodes 2 are formed on a transparent support substrate 1 into stripes at a predetermined interval, and a hole transport layer 3 is formed on the transparent support substrate 1 and transparent electrodes 2. As shown in FIG. 8A, a red-emitting layer 4a, green-emitting layer 4b, and blue-emitting layer 4c are formed on the hole transport layer 3 alternately to correspond to the transparent electrodes 2, such that they are parallel to the transparent electrodes 2. An electron transport layer 5 is formed on the red-emitting layer 4a, green-emitting layer 4b, and blue-emitting layer 4c. A plurality of metal electrodes 6 are formed on the electron transport layer 5 into stripes in a direction perpendicular to the transparent electrodes 2.
In this arrangement, when the transparent electrodes 2 are set at a positive voltage and a DC voltage is applied across the transparent electrodes 2 and metal electrodes 6, portions where the transparent electrodes 2 and metal electrodes 6 overlie each other emit light. These light-emitting overlying section are used as pixels.
A method of manufacturing the color organic thin film EL panel having the above arrangement will be described.
A transparent conductive film made of ITO or the like is formed on the transparent support substrate (to be referred to as the transparent substrate hereinafter) 1 made of glass or the like by sputtering, and then the transparent electrodes 2 are formed into stripes by photolithography and wet etching. TPD or the like is vacuum-deposited to form the hole transport layer 3 covering the transparent substrate 1 and transparent electrodes 2. The red-emitting layer 4a, green-emitting layer 4b, and blue-emitting layer 4c are sequentially formed on the hole transport layer 3 by using a shadow mask scheme to be parallel to the transparent electrodes 2, such that they are adjacent to each other in this order. Tris(8-quinolilite)aluminum or the like is vacuum-deposited to form the electron transport layer 5 on the red-, green-, and blue-emitting layers 4a to 4c. 
A metal mask having striped openings is formed on the transparent substrate 1 on the electron transport layer 5 side such that its openings are perpendicular to the transparent electrodes 2. Metals, e.g., magnesium and silver, or lithium and aluminum, having small work functions are deposited simultaneously to form the metal electrodes 6. The metal mask is then removed, and a protection film (not shown) made of an inorganic material such as SiO2, or an organic material such as a fluoroplastic is formed by sputtering. Finally, to prevent humidity invasion, a sealing plate such as a glass plate is adhered with a low-hygroscopic photosetting adhesive, epoxy-based adhesive, or silicone-based adhesive or the like, thereby hermetically sealing the obtained structure.
The metal electrodes are formed by vacuum deposition using the metal mask due to the following reason. Since the organic thin film is not resistant to water and has a low durability against an organic solvent or chemicals, pattern formation by photolithography and wet etching cannot be performed.
In the metal electrode forming method described above, since the metal is deposited in stripes, the electrodes and interconnections are formed integrally. The film thickness cannot be increased to prevent pixel portions from being damaged by heat radiated during metal vapor deposition. Therefore, the interconnection resistance of the metal electrodes increases. Also, the interconnection resistance changes depending on the positions of the pixels, resulting in variations in brightness of the pixels. To prevent these problems, conventionally, even after the alloy to form the electrodes is deposited, deposition of the metal having a lower resistivity is continued to decrease the interconnection resistance.
In the metal electrode forming method described above, the alloy must be deposited at a low deposition rate so that the mixing ratio of the alloy becomes constant. This prolongs a time required for electrode formation. Since the metal having a lower resistivity is continuously deposited, heat radiated from the vapor source increases the substrate temperature to be equal to the glass transition temperature or more of the organic film. Then, the organic film may agglomerate to form corrugations on its surface, or a pinhole may be formed in the film to short-circuit the transparent electrodes and the metal electrodes.
It is an object of the present invention to provide an organic thin film EL panel having a metal electrode having a low interconnection resistance, and a method of manufacturing the same.
It is another object of the present invention to provide an organic thin film EL panel in which glass transition of an organic film caused by heat radiated from a vapor source during metal electrode formation is prevented, and a method of manufacturing the same.
In order to achieve the above object, according to the present invention, there is provided an organic thin film EL panel comprising a plurality of transparent electrodes formed into stripes on a transparent substrate, an organic deposition film including a light-emitting layer and formed on the transparent substrate and the transparent electrodes, and a plurality of metal electrodes formed into stripes on the organic deposition film in a direction perpendicular to the transparent electrodes, the metal electrodes being comprised of a plurality of electrode portions arranged at a predetermined interval, and a plurality of interconnections that connect adjacent ones of the electrode portions to each other, the electrode portions having pixel regions where the metal electrodes and the transparent electrodes overlie each other, and connection regions other than the pixel regions, and the interconnections connecting the connection regions of adjacent ones of the electrode portions to each other.